B757 Hydraulics
Good morning everybody.
Back to study,and once again on Hydraulics,some questions raised and I kow there is no question that cannot be answered here(by experience) so I hope to don t bother too much.
Here they are:
1-Boeing QRH says"Autobrake INOP" if R Hyd failure.Ok.Nut wy it sys:"DO NOT USE AUTOBRAKE" when L Hyd failure?what do they mean?Because if you only loose L Hyd,you still have R Hyd so you have Normal and Reserve Brakes so we should have full Autobrake capability..
2-If we loose R Hyd,we ll only have Alt Brakes(with only laterally paired antiskid capability).Why then there is nothing on QRH saying that anti-sid action will be reduced?
3-Why QRH says "Do not arm Speedbrakes· everytim we loose 2 Hydraulics?
4-What is the real reason to have a "DO NOT AUTOLAND" with only 1 Hyd falure?because we have 3 HYDS required for Cat 3B,but only 2 HYDS required for Cat 2,and from cat 2 we can land either manual or Autoland.So does it means that with one HYD failure we are limited to Cat 2(300m) and that we ll have to lad manually?And why?what is the change from disconnecting or not the A/P just before landing?
5-RAT gives enough power above 130 kts.Ok.What about below?Being ligh Vref will be below 120 so does it means that rudder will be almost useless on the last portion of the approach?
6-When we are nt using Flaps or Gear(high demand),are the Demand Elec umps C1 and C2 working at all?or they re just waiting on a low Pressure?
7-And my favorite:CANCELLING the PARKING BRAKE EICAS message before taxi.Let s say we lost Antiskid and let s say we cancel the message without waiting to see the message disappearing when we release Parking Brake.And lets say we don t put the PB anymore during Taxi.We could then hide the Anti-skid problem?So it s not a good idea at all to ancel it.Actually Boeing says "Recall/cancel" before start but only"Recall" before taxi.Is that the reason.
And,if that s the case,if PARKING BRAKE EICAS(being PB released) means Anti-skid failure because the valves are the same,what does ANTISKID EICAS message means?What is he difference?
Thanks so much,I hope somebody will find it interesting.Good flights